1. Field of the Invention
The present invention relates to an opening and closing device, a sheet conveying apparatus, and an image forming apparatus, and more particularly to a constitution for opening and closing an opening and closing portion constituted by a fixed side member and a movable side member.
2. Related Background Art
Conventionally, for example, in an image forming apparatus such as a printer, a fax machine, a copier, or a printing press, images are formed by an image forming method such as an electrophotographic process, an offset printing method, or an ink-jet method. As an example of such an image forming apparatus, there is a color image forming apparatus that forms color images by the electrophotographic process. Such a color image forming apparatus adopts a tandem method in which a plurality of image forming units constituting an image forming portion are arranged side by side, a rotary method in which a plurality of image forming units are cylindrically arranged, or the like. A transfer method for such a color image forming apparatus is classified into a direct transfer method in which a toner image is directly transferred from a photosensitive member onto a sheet and an intermediate transfer method in which a toner image is transferred first onto an intermediate transfer member and then onto a sheet.
Herein, in an intermediate transfer tandem method in which a plurality of (four) image forming units are arranged side by side on an intermediate transfer belt, there is no need to retain a sheet on a transfer drum or a transfer belt unlike the case of the direct transfer method. Therefore, the intermediate transfer tandem method is advantageous in that a great variety of sheets including ultra-thick papers and coated papers can be dealt with and that a sheet path to a secondary transfer portion for transferring an image onto a sheet from the intermediate transfer belt can be simply structured. Moreover, since the degree of freedom in stretching the intermediate transfer belt is high, the intermediate transfer tandem method is advantageous in reducing the size of the image forming apparatus as well.
In addition to the above-mentioned merits, the tandem method offers a highly advantageous constitution in accomplishing speedup because of its features including a parallel processing in a plurality of image forming units and a batch transfer of full-color images. Therefore, the tandem method is suited for a color image forming apparatus, which is targeted for high productivity.
In such a color image forming apparatus, it is necessary to have access to a relevant portion from the outside of the apparatus during replenishment, replacement, and service maintenance of consumables, or during an operation of removing a sheet etc., at the time of jamming. For this reason, the color image forming apparatus is provided with various opening and closing portions. Further, in the case where the color image forming apparatus is provided with an original reader, this original reader is provided with an original pressure cover as an opening and closing portion. In using the original reader, a user operates the original pressure cover in its opening and closing directions.
For such an opening and closing portion, there have been proposed various opening and closing devices that are intended to prevent a damage from being caused by a dropping impact of a movable side member such as a door, to reduce the load imposed on an operator, and so forth. Herein, some of the simplest ones of such opening and closing devices are provided with a wire member (a wire, a rope, a chain, a ribbon, or the like) which also serves to regulate an opening and closing angle so as to prevent the opening and closing portion from opening beyond a certain angle. In the opening and closing device as described above, however, the wire member may be fractured due to an impact unless the movable side member to be opened and closed is light or the opening and closing angle is relatively small.
On this account, if the movable side member to be opened and closed is heavy, an opening and closing device equipped with a shock absorber such as a damper is often employed. Herein, such an opening and closing device is broadly classified into three types depending on where the shock absorber is installed.
In the first type, a shock absorber supports a turning end of a movable side member such as a door, which is open, for example, after having been turned downwards. This type has a merit in that since the neighborhood of the turning end which is most distant from a turning center of the movable side member is supported, the force required for support can be held relatively small even when the movable side member is heavy (e.g., as disclosed in Japanese Patent Application Laid-Open No. H11-84791).
In the second type, a shock absorber is provided at a turning center of a movable side member. This type has a merit in that since there is no need to provide the turning end with a support portion, an ample open space with a clean-cut constitution can be achieved (e.g., as disclosed in Japanese Patent Application Laid-Open No. 2003-15237).
In the third type, a member interlocking with a movable side member is provided with a shock absorber. This type has a merit in that since the location for installing the shock absorber is not particularly limited to an opening or a turning center, a high degree of freedom in layout is obtained (e.g., as disclosed in Japanese Patent Application Laid-Open No. H11-84982).
However, in an opening and closing device and an image forming apparatus provided with the conventional shock absorber as described above, for example, in the case of the opening and closing device disclosed in Japanese Patent Application Laid-Open No. H11-84791, there is a problem in that the opening and closing device cannot be easily applied to an opening and closing portion with a limited vertical dimension in particular because of a large installation space for a damper.
Further, in the case of the opening and closing device disclosed in Japanese Patent Application Laid-Open No. 2003-15237, the installation space for the damper can be reduced by providing the damper at the turning center (i.e., on the turning shaft). However, since the largest load is imposed on the turning center in supporting the movable side member, the required torque capacity increases and the size of the damper also increases as the weight of the movable side member increases. Thus, the hinged structure is enlarged in size, which causes a problem in that it is difficult to reduce the thickness of the opening and closing device.
Further, the opening and closing device disclosed in Japanese Patent Application Laid-Open No. H11-84982 adopts a method in which the load applied to the rotary damper is dispersed by providing an interlocking member interlocking with the movable side member with the rotary damper and an extension spring as auxiliary damper means. However, if the opening and closing portion is a sheet conveying passage, for example, a rigid body such as the interlocking member must be structured not to shut off the sheet conveying passage when a guide plate or the like constituting the sheet conveying passage is closed.
In the case of such a structure, however, the space required for other members than the sheet conveying passage increases and consequently, the sheet conveying apparatus is considerably enlarged in size. Furthermore, in a place requiring a large opening and closing angle, since the length of the interlocking member or the operating length of the extension spring increases, the space required for opening and closing operations increases in either case.
On the other hand, as a rule, in the case where high productivity, high reliability, and high durability are especially demanded of an image forming apparatus, its respective units demonstrate high rigidity and tend to increase in size and weight. In the case of such an image forming apparatus, it is also necessary to give careful consideration to what does not raise a serious problem in the field of office equipments and the like, for example, an opening and closing operational force that is applied in coping with the jamming of the sheet conveying passage.
Further, in the case where the sheet conveying passage is disposed in a lower portion of the image forming apparatus, since a user assumes a stooping posture in coping with the jamming of the apparatus, it is highly necessary to lighten the load imposed on the user. In addition, as the productivity of the image forming apparatus is enhanced, the image forming portion and the like increase in size and become complicated, and enhancement of the capacity of a sheet feeding device is also desired. From the standpoint of usability, however, the position of an operating portion or the height of the image forming apparatus body cannot be changed with ease. Therefore, it takes on great significance how to reduce the thickness and size of the opening and closing device for opening and closing the opening and closing portion such as the sheet conveying passage.